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Author Topic:   How much HP will I lose installing auto tranny?
662+2
Journeyman

Posts: 55
From: Ontario, Canada
Registered: Jan 2003

posted 01-15-2003 07:09 PM     Click Here to See the Profile for 662+2   Click Here to Email 662+2     Edit/Delete Message   Reply w/Quote
IF I take out my 3 speed standard and install a C4 how much Hp will I lose and how much will it slow down my car

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clevelandstyle
Gearhead

Posts: 494
From: Connersville, IN
Registered: Jul 2001

posted 01-15-2003 08:02 PM     Click Here to See the Profile for clevelandstyle     Edit/Delete Message   Reply w/Quote
Although you may loose a small amount of HP from converter slippage, the 3 speed manual gearing is probably not optimized for the strip. With a decent converter the car would likely go quicker with a C4.

------------------
Ben
Grabber Green '70 Mach I 351C 4V
Robbin Egg Blue '79 Fairmont 351C 4V

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Moneymaker
Administrator

Posts: 18704
From: Lyons, IL, USA
Registered: May 99

posted 01-15-2003 09:01 PM     Click Here to See the Profile for Moneymaker   Click Here to Email Moneymaker     Edit/Delete Message   Reply w/Quote
You won't lose any horsepower at all. If you don't use any tpe of stall converter, you may lose some ET, but no HP.

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Alex Denysenko
Co-Administrator and Moderator

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662+2
Journeyman

Posts: 55
From: Ontario, Canada
Registered: Jan 2003

posted 01-15-2003 09:07 PM     Click Here to See the Profile for 662+2   Click Here to Email 662+2     Edit/Delete Message   Reply w/Quote
What converter should I use for a C4?

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steve'66
Gearhead

Posts: 5659
From: Sonoma,CA,USA
Registered: Mar 2000

posted 01-15-2003 10:26 PM     Click Here to See the Profile for steve'66   Click Here to Email steve'66     Edit/Delete Message   Reply w/Quote
When we went from a 3 speed (w/od) tranny in the '66 (back when it had a 351w) we went from a best of 12.58 to a 12.002 with a race c-4 with 4000 stall converter.
I wouldn't worry about slowing down with the right tranny and a quality converter.

SteveW

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mustangboy
Gearhead

Posts: 520
From: Ont, Canada
Registered: Mar 2002

posted 01-16-2003 12:46 AM     Click Here to See the Profile for mustangboy     Edit/Delete Message   Reply w/Quote
Are we saying a stock automatic doesn't take anymore hp to turn than a standard.

[This message has been edited by mustangboy (edited 01-16-2003).]

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Rory McNeil
Gearhead

Posts: 1098
From: Surrey, B.C. Canada
Registered: Nov 2000

posted 01-16-2003 04:03 AM     Click Here to See the Profile for Rory McNeil   Click Here to Email Rory McNeil     Edit/Delete Message   Reply w/Quote
Yes, an automatic certainly absorbs more power on it`s way to the rear wheels, but the actual ENGINE horsepower doesn`t change.As for switching the 3 speed to a C4, as Steve said, a 3 speed manual is hardly ideal for drag racing, but instead of joining the "icky red fluid automatic gang" I believe your best bet would be to install a T5 5speed from a 5.o Mustang. With the right adapter, you can use your existing clutch & bellhousing, & clutch linkage. I`m sure you could find a decent used T5 & the adapter, & preferably an aftermarket shifter for less than a rebuilt C4 with a high stall convertor, cable shifter & trans cooler. About 6 years ago, I swapped out the C4 in my 302 Fairmont streeter, to a stock T5, & I picked up almost a full second in the 1/4 mile over the auto, which had a 2800 rpm stall convertor. In addition to the much better ET`s (from a 13.72 best with the auto, to 12.80 with the 5 speed), it also knocked almost 1000 rpm of my freeway cruise revs. Most 5.0 Mustang T5`s have a 3.35 low gear, which is much better than a toploader 4 speeds 2.78 or 2.32 1rst. Plus the overdrive, PLUS it`s lighter, PLUS it shifts easier! Driving a non OD equipped automatic with a loose convertor every day gets pretty old in a hurry, not to mention the fear of freeways, when combined with fairly low rearend gears. If you were to put a stock C4 with a stock convertor in your Mustang, I`m sure it would slow down at least 2 or 3 tenths, maybe more. A 5 speed would likely lower your ET by at LEAST that amount, if not more. Do you want to ENJOY racing your car, OR do you want to play with the radio & eat a sandwich while going downtrack?

------------------
78 Fairmont 428 4 speed [email protected]
80 Fairmont 302 5 speed [email protected]
85 Mustang NHRA Stocker under construction, 302 5 speed
59 Meteor (Canadian Ford) 2 dr sedan 332, auto
74 F350 ramp truck 390 4spd

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662+2
Journeyman

Posts: 55
From: Ontario, Canada
Registered: Jan 2003

posted 01-16-2003 05:46 PM     Click Here to See the Profile for 662+2   Click Here to Email 662+2     Edit/Delete Message   Reply w/Quote
Thanks guys for the info but I still am undecided

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662+2
Journeyman

Posts: 55
From: Ontario, Canada
Registered: Jan 2003

posted 01-16-2003 06:30 PM     Click Here to See the Profile for 662+2   Click Here to Email 662+2     Edit/Delete Message   Reply w/Quote
Oh ya I like racing my car and I like shifting gears. I do think that you are right about having the 5th gear for driving on the street because with my 3.8 gears in the back it sure likes to rev on the highway.Steve how much hoursepower did you have in that 351 to run that 12.00 with the C4?

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steve'66
Gearhead

Posts: 5659
From: Sonoma,CA,USA
Registered: Mar 2000

posted 01-16-2003 06:51 PM     Click Here to See the Profile for steve'66   Click Here to Email steve'66     Edit/Delete Message   Reply w/Quote
Never had it dyno'd but the powerplant was the same with both 3 speed manual and auto. I'll guess the 351w made around 375+ fwhp, it could have run in the high 11's but we were fighting a bogging problem off the t-brake with the little 351w engine. 60's were slow We only ran this combo once, before the 408w was ready. Then it went 10.82 with the added weight of a roll bar, and the same converter that stalled at 4000 behind the 351w stalls at 4600 with the 408w.

As a side note we tried a t-5 too and it's best was a 12.68 with the same engine. The t-5 did manage to break the 9"rear once and roll the spring perches another time. Too low a first gear,

Your results may vary

SteveW

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662+2
Journeyman

Posts: 55
From: Ontario, Canada
Registered: Jan 2003

posted 01-16-2003 07:24 PM     Click Here to See the Profile for 662+2   Click Here to Email 662+2     Edit/Delete Message   Reply w/Quote
This might be a stupid question but why would a low first gear break the 9" and is this something I should worry about if I was to install into my car.

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steve'66
Gearhead

Posts: 5659
From: Sonoma,CA,USA
Registered: Mar 2000

posted 01-16-2003 08:58 PM     Click Here to See the Profile for steve'66   Click Here to Email steve'66     Edit/Delete Message   Reply w/Quote
Because total gear ratio multiplies torque and torque is the leverage on the rear tires. The track was very sticky and traction wasn't a problem.
So with a 1st gear ratio of say 3.3-1 times a rear gear ratio of 4.1-1 equals an overall ratio of 13.53-1. Which means that if you launch with the engine producing 400 ft pounds of torque it's multiplied by 13.53 and results in the rear tires (and the rear end) being hit with 5,412 ft pounds of torque. Thats like puting a 20" breaker bar on the center of your rear axle and droping a mustang on it.

Torque converters are much easier on parts.

Again, your results may vary.

SteveW

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MrWesson22
Gearhead

Posts: 1103
From: Dacula, GA
Registered: Sep 2000

posted 01-16-2003 09:01 PM     Click Here to See the Profile for MrWesson22   Click Here to Email MrWesson22     Edit/Delete Message   Reply w/Quote
Deeper gears = more torque multiplication = harder on rearends. But a T5 transmission should break long before the 9" behind it does. A 3.27 or 3.35 1st gear in a T5 depending on model is obviously much deeper than a 2.46 1st in a C4. If you had a T5 in your car, with the 3.80 gears, it would launch like a C4 would with 5.00 gears.

------------------
Neal

69 Gulfstream Aqua Grande
351C/4sp
https://mustangsandmore.com/ubb/MrWesson22.html

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steve'66
Gearhead

Posts: 5659
From: Sonoma,CA,USA
Registered: Mar 2000

posted 01-16-2003 09:54 PM     Click Here to See the Profile for steve'66   Click Here to Email steve'66     Edit/Delete Message   Reply w/Quote
Neal,

Don't forget the shock of droping a centerforce clutch spinning at 4,000 rpms hits the rear with. The t-5 survived fine, and is still running around in Matt's stang. Is the pic of the 9" still on this site in the archives somewhere? It threw the pinion out the side of the case.

SteveW

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TomP
Gearhead

Posts: 4637
From: Delta BC Canada
Registered: Dec 99

posted 01-16-2003 10:16 PM     Click Here to See the Profile for TomP   Click Here to Email TomP     Edit/Delete Message   Reply w/Quote
If you think it revs high on the highway now with 3.8's and a 3 speed, wait till you see what it does with a slusher and high stall pervertor. You can expect an extra couple hundred rpm. On trucks used for towing it gets way worse, it can actually rev less with 4.56's than 4.10's because it isn't as heavily loaded and further from the stall speed.

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MrWesson22
Gearhead

Posts: 1103
From: Dacula, GA
Registered: Sep 2000

posted 01-16-2003 10:33 PM     Click Here to See the Profile for MrWesson22   Click Here to Email MrWesson22     Edit/Delete Message   Reply w/Quote
Yeah Steve, I LOVE that feeling! Of course, from what I hear, a good transbrake and high stall hits pretty well too, but it can't be like sidestepping the clutch at WOT.

------------------
Neal

69 Gulfstream Aqua Grande
351C/4sp
https://mustangsandmore.com/ubb/MrWesson22.html

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jsracingbbf
Gearhead

Posts: 1217
From: Batesville,MS. , U.S.A.
Registered: Mar 2002

posted 01-17-2003 12:02 AM     Click Here to See the Profile for jsracingbbf   Click Here to Email jsracingbbf     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by 662+2:
Thanks guys for the info but I still am undecided


Gee I wonder why? Do you think you have enough different opinions? Ray charles coulda seen this coming.

Jerry

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